JP 2009-159653 A discloses an illuminating system which includes an illuminating fixture electrically and directly connected to a DC line in a residence or an illuminating fixture electrically connected to a DC line through a wiring device such as a ceiling-mounted socket. Such DC lines each include two DC power supply paths, and are electrically connected to an AC/DC converter provided to a residential power distribution panel. Further, such illuminating fixtures each include a light source powered by a DC voltage to light (emit light) such as a light emitting diode (LED) or organic electroluminescence element. Since the illuminating fixture is powered by DC power supplied through the DC power supply paths, the illuminating fixture need not include a power supply circuit such as an AC/DC converter for converting an AC voltage into a DC voltage.
In the conventional illuminating system described above, the illuminating fixture may be attached to the DC power supply path under live-line state (which is energized), but an input terminal of an illuminating fixture and a conductor of the DC power supply path may become incompletely connected. When a large current flows from the conductor of the DC power supply path to the input terminal of the illuminating fixture under the incomplete connection between the conductor of the DC power supply path and the input terminal of the illuminating fixture, an electric arc may be formed between them. Once the electric arc is formed, to extinguish such an electric arc is more difficult for the conventional illuminating system described above than for an illuminating system that receives an AC voltage.